Continuous cardiac output monitor

ABSTRACT

A device for continuously monitoring the output of a heart in a surgical patient includes a probe head attached at one end to a catheter adapted to be inserted into the patient. The probe head includes a probe and a pair of flexible flat projections extending outwardly from opposite sides of the probe for securing the probe head in the transverse sinus of the patient. At least one transducer is positioned in the probe for detecting a condition of the heart. A hollow needle is adapted for receiving the probe head prior to its installation in the patient, such that the probe head can be installed in the patient immediately after mediansternotomy and division of the patient&#39;s pericardium by inserting the needle through the patient&#39;s chest wall. A method for continuously monitoring the condition of the heart in a surgical patient includes the steps of providing a probe head responsive to heart function; positioning the probe head in the transverse sinus of the patient proximal to the aortic valve and behind the ascending aorta; and displaying an output of the probe head reflective of the heart condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to cardiac monitoring, and more particularly to amethod and device for monitoring the output of a heart during postoperative open heart surgery.

2. Description of the Related Art

Cardiac output monitoring has been performed on most open heart surgerypatients since the development of the intravascular thermodilution (T-D)cardiac output catheter over 20 years ago. The Swan-Ganz catheter is oneform of a T-D style catheter and is the current standard for cardiacoutput measurement. T-D style catheters are positioned intravascular,typically inserted into the jugular vein and threaded into the heart.Such a catheter calculates estimated cardiac output intermittently bymeasuring externally induced fluid temperature differentials within thepulmonary artery (on the right side of the heart) to measure flowvelocity during the cardiac cycle and then assuming the value isindicative of left side heart function. The flow velocity is determinedby calculating an average for 3-4 temperature inducements over a 4-5minute period.

The use of T-D catheters is subject to many variables including operatorerror, injectate temperature variances, speed and timing of the coldfluid injection, etc. Although not accurate in measurement, the valuesgenerated by this technique are generally and historically accepted as arelative depiction of cardiac performance.

Besides their measurement inaccuracy, which is estimated at ±20%, T-Dcatheters currently in use are relatively expensive and are notinnocuous. The medical literature has documented the side effects andcomplications associated with these intravascular catheters in greatdetail. Among the more serious complications are pulmonary arteryrupture, increased infection rate, arrhythmias, difficult insertion andremoval resulting in catheter body knotting or catheter balloonrupturing, intracardiac trauma to valves and ventricles, cardiacperforation, high risk of fluid overload, etc.

A recent improvement is a "continuous output" T-D catheter that featuresa modified Swan-Ganz design by adding an electrical temperature filamentto the distal end of the catheter. It induces electrically generatedtemperature differentials into the fluid path thereby eliminating theneed to inject a cold solution into the blood stream. This device readsthe subtly induced temperature changes in the fluid path during thecardiac cycle to calculate flow velocity. The eventual readout is anaverage reading of data gathered over a 30 second to one minuteinterval.

As described in U.S. Pat. No. 4,671,295, it is known to use a pair ofDoppler crystals for measuring volumetric blood flow in the aorta. TheDoppler crystals also measure the changes in aortic diameter with eachbeat of the heart.

Other techniques occasionally reported for use in monitoring continuouscardiac output include Trans Esophageal Echocardiographic measurement(TEE) and the IQ System (Renaissance Technologies, Newton, Pa.), whichemploy thoracic electrical impedance measurement and time-frequencysignal processing to compute cardiac output.

There exists a continuing need for a more accurate, cost-effective, andcontinuous output-type catheter for perioperative cardiac management.The present invention substantially fulfills that need.

SUMMARY OF THE INVENTION

These and other problems of the prior art are overcome by the provisionof a device for continuously monitoring the output of a heart in asurgical patient. According to one aspect of the invention, a probe headassociated with one end of a catheter is adapted for insertion into apatient. The probe head includes a probe and a pair of flexible fiatprojections extending outwardly from opposite sides of the probe forsecuring the probe head in the transverse sinus of the patient. At leastone transducer is positioned in the probe for detecting a condition ofthe heart.

According to another aspect of the invention, a hollow needle is adaptedfor receiving the probe head prior to installing the probe head in thepatient, such that the probe head can be installed in the patientimmediately after mediansternotomy and division of the patient'spericardium by inserting the needle through the patient's chest wall.

According to one feature of the invention, a method for continuouslymonitoring the condition of the heart in a surgical patient includes thesteps of providing a probe head responsive to heart function;positioning the probe head in the transverse sinus of the patientproximal to the aortic valve and behind the ascending aorta; anddisplaying an output of the probe head reflective of the heartcondition.

According to a further feature of the invention, a method forcontinuously monitoring the condition of the heart includes theprovision of a probe head that is capable of monitoring both the bloodcenterline velocity of the aorta and changes in the aortic diameter inreal time.

According to an even further feature of the invention, the probe head issecured to the transverse sinus with releasable sutures, and thecatheter body is secured at a position distal from the heart withabsorbable sutures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings inwhich:

FIG. 1 is a perspective view of a cardiac monitoring catheter accordingto the invention;

FIG. 2 is a top view of an exposed heart of a patient during open heartsurgery and illustrating insertion of the cardiac monitoring catheter ofFIG. 1;

FIG. 3 is a view similar to FIG. 2 showing the catheter tip exposed forpositioning behind the ascending aorta;

FIG. 4 is an enlarged view of the exposed heart showing placement of thecardiac monitoring catheter; and

FIG. 5 is an enlarged view of the catheter trailing end secured to thepatient's outer epidermis layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, the cardiac monitoring catheter 10 comprises asmall, elongated flexible body 12 having a distal end 16 whichterminates at a probe head 14. The probe head 14 comprises a probe 15and a pair of flexible flat wings 22 that project outwardly fromopposite sides of the probe 15. A pair of Doppler crystals 18, 20 areimpregnated into the probe 15. One of the crystals measures the centerline velocity of the blood passing through the aorta while the othercrystal measures changes in the aortic diameter with each beat of theheart. The wings, together with the probe, form a cobra head-shapedstructure. Each wing 22 features a tiny suture port 24 for receiving atleast one suture to anchor the probe head 14 against movement oncepositioned in the body of a patient. The overall length of the catheter10 is preferably 24 inches. However, the catheter may be sized in otherlengths depending on individual requirements of the patient.

A proximal end 26 of the wire 12 terminates in a standard dual coaxialelectro-mechanical connector 28 that interfaces with a monitor 30.Suitable electrical signal conduits extend between the Doppler crystals18, 20 and the connector 28. The monitor 30 is preferably a backlitliquid crystal display. A reusable (sterilizable) extension cable 32(shown in dashed line) is used to interconnect the connector 28 and themonitor 30. The monitor 30 is associated with well-known circuitry (notshown) for energizing each Doppler crystal and for interpreting eachcrystal's response. The monitor may be positioned at the head of thesurgical table for anesthesia access or positioned at the patient'sbedside in the intensive care unit. The monitor may provide dataparameter readouts in the form of multiple display options such ascontinuous cardiac output, cardiac index, aortic diameter, center linevelocity of the blood through the aorta, and blood flow wave form.Slaved-in parameters include systemic vascular resistance (SVR) andarterial pressure. The monitor may be associated with a keypad (notshown) for entering patient parameters or may be pre-programmed withparameters such as body surface area (BSA), which is necessary tocompute the cardiac index.

FIGS. 2-5 show the process for mounting the probe 14 in a patient.First, the probe 14 and wings 22 are received telescopically within ahollow needle 34, such as the DLP Scabbard™ Needle having an inserter orgrip 36 provided thereon. The flexibility of the wings 22 permit them tobe wrapped around the probe 14 when positioned in the needle 34. In use,the grip 36 is grasped by a surgeon's hand and the needle 34 with theattached catheter 10 are inserted through the chest wall 40 of a patientand into the open mediastinum 42, as seen in FIG. 2. Once the needle 34and at least a portion of the catheter body 12 have been insertedthrough the chest wall, the needle 34 is separated from the catheterbody 12, as seen in FIG. 3. In order to effectively determine cardiacoutput, the probe head 14 must be accurately positioned within themediastinum 42. Preferably, the probe head 14 is positioned in thetransverse sinus, behind the ascending aorta 44 and close to the aorticvalve, as seen in FIG. 4. In this position, accurate readout of cardiacoutput is easily and safely obtained. The weight and anatomical positionof the aorta alone lends itself to holding the probe head 14 securely inplace. However, it is preferred that the probe head 14 be additionallysecured to the posterior pericardial reflection with two 7-0sutures 46placed through the suture ports 24 in the winged projections 22.Securing the probe head 14 in this fashion prevents the probe head fromshifting while in use and permits easy and safe post-operative removal.The remaining catheter body 12 is secured to the lateral pericardialwall 48 using absorbable sutures 50 similar to an LA line securingtechnique. The sutures 50 act as a guide for the catheter when beingremoved, to prevent interference between the catheter and any veingrafts or cardiac structures. The catheter body 12 is then secured tothe outer epithelial layer 52 of the chest wall 40 using a catheteranchoring collar 54, as seen in FIG. 5. The collar 54 may be secured tothe epithelial layer 52 either through adhesive, tape, or sutures.

In order to remove the catheter 10, the anchoring collar 54 is firstremoved from the outer epithelial layer 52. The surgeon then simplypulls on the catheter body 12 until the 7-0 sutures 46 separate. Thiseliminates the need for a suture severing mechanism and preventspossible damage to the aorta as in the prior art. As the catheter 10 iswithdrawn through the chest wall 40, the catheter body 12 and probe head14 are guided around the pericardium 48 by the guide sutures 50, therebykeeping the catheter from snagging any vein grafts or cardiacstructures. The catheter 10 is preferably removed from the closedmediastinum 24-72 hours post-operatively, prior to the removal of anychest tubes associated with the open heart surgery.

Unlike the prior art devices, the catheter 10 of the present inventioncan be inserted and positioned in the surgical patient immediately aftermediansternotomy and division of the pericardium. In most cases thecatheter 10 can be in position and operational in a matter of three tofive minutes after skin incision. The catheter is inserted across thechest wall, into the open mediastinum and quickly positioned and securedin the transverse sinus under direct visualization. Once in position,baseline hemodynamic parameters can be obtained immediately by theanesthesiologist. The catheter 10 remains in position and out of the wayduring the surgical procedure. As the surgical repairs are completed,the catheter can resume functioning immediately as the patient iswithdrawn from cardiopulmonary bypass, giving the surgical team areal-time picture of returning cardiac function. The prior art catheterscannot be positioned or used until the mediastinum is ready to beclosed. In using the catheter 10 according to the invention, theanesthesiologist can utilize a CVP line (a current standard of practice)to administer fluids and pharmaceuticals. The catheter 10 can also beused in conjunction with a T-D catheter as well as an LA line onextremely critical patients.

Because the catheter 10 is not used intravascularly, this inventioneliminates most of the problems and their related costs associated withT-D catheters. The catheter 10 according to the invention is more costeffective to operate and use as it does not require any operation otherthan an on/off switch. The catheter 10 of the present invention thusprovides a level of accuracy and reliability far exceeding that of a T-Dcatheter without any of the related risks, side effects and resultantcosts.

Reasonable variation and modification are possible within the spirit ofthe foregoing specification and drawings without departing from thescope of the invention.

The embodiments for which an exclusive property or privilege is claimedare defined as follows:
 1. A system for continuously monitoring theoutput of a heart in a surgical patient, comprising:a catheter having aproximal end and a distal end, the proximal end being adapted forelectrical connection to a display; a probe head provided on thecatheter, the probe head including a probe and a pair of flexible flatprojections extending outwardly from opposite sides of the probe forsecuring the probe head in the transverse sinus of the patient, each ofthe flexible projections having an outer edge portion; at least onetransducer positioned in the probe for detecting a condition of theheart; and a hollow needle adapted for receiving the probe head prior toinstalling the probe head in the patient, an inner diameter of thehollow needle being smaller than the distance between the outer edgeportions of the flexible projections; whereby the probe head can beinstalled in the patient immediately after mediansternotomy and divisionof the patient's pericardium by inserting the needle through thepatient's chest wall.
 2. A system according to claim 1 wherein theprojections are wrapped around the probe when the probe head is receivedwithin the needle.
 3. A system according to claim 1 wherein eachprojection includes an aperture for receiving at least one suture foranchoring the probe head against movement with respect to the body of apatient.
 4. A system according to claim 1 wherein the projections andthe probe together form a cobra head shape.
 5. A system according toclaim 1 and further in combination with the body of a patient having anascending aorta, a transverse sinus located behind the aorta, and anaortic valve located adjacent the ascending aorta, and further whereinthe probe head is adapted to be positioned in the transverse sinusbehind the ascending aorta and in proximity to the aortic valve.
 6. Acombination according to claim 5 and further comprising a pericardialreflection posterior of the ascending aorta, and wherein the probe headis adapted to be sutured to the pericardial reflection.
 7. A combinationaccording to claim 6 wherein each projection includes an aperture forreceiving at least one suture for anchoring the probe head to thepericardial reflection.
 8. A combination according to claim 7 whereinthe at least one transducer is oriented in the probe for measuring atleast one of a centerline velocity of blood passing through the aortaand a change in diameter of the aorta during heart beating.
 9. A systemfor continuously monitoring the output of a heart in a surgical patient,comprising:a catheter having a proximal end and a distal end, theproximal end being adapted for electrical connection to a display; aprobe head provided on the catheter, the probe head including a probeand a pair of flexible wings extending outwardly from opposite sides ofthe probe for securing the probe head in the transverse sinus of thepatient; at least one transducer positioned in the probe for detecting acondition of the heart; and a hollow needle adapted for receiving theprobe head prior to installing the probe head in the patient, the wingsof the probe head being wrapped around at least a portion of the probewhen the probe head is received within the needle; whereby the probehead can be installed in the patient immediately after mediansternotomyand division of the patient's pericardium by inserting the needlethrough the patient's chest wall.
 10. A system according to claim 9wherein each projection includes an aperture for receiving at least onesuture for anchoring the probe head against movement with respect to thebody of a patient.
 11. A system according to claim 9 wherein theprojections and the probe together form a cobra head shape.
 12. A systemaccording to claim 9 and further in combination with the body of apatient having an ascending aorta, a transverse sinus located behind theaorta, and an aortic valve located within the ascending aorta, andfurther wherein the probe head is adapted to be positioned in thetransverse sinus behind the ascending aorta and in proximity to theaortic valve.
 13. A combination according to claim 12 and furthercomprising a pericardial reflection posterior of the ascending aorta,and wherein the probe head is sutured adapted to be to the pericardialreflection.
 14. A combination according to claim 13 wherein eachprojection includes an aperture for receiving at least one suture foranchoring the probe head against movement to the pericardial reflection.15. A combination according to claim 14 wherein the at least onetransducer is oriented in the probe for measuring at least one of acenterline velocity of blood passing through the aorta and a change indiameter of the aorta during heart beating.